Polyolefin-based wrapping film

Abstract

A polyolefin-based wrapping film having one or more layers which satisfies the following conditions (1) to (4): (1) the film has a thickness ranging from 6 to 100 mu m; (2) the film has a birefringence DELTA nA of from 0.6x10-3 to 8x10-3; (3) the film has a ratio of percent heat shrinkage in MD to percent heat shrinkage in TD of from 0.65 to 1.50 in a silicon oil bath at 140 DEG C. for 3 minutes; and (4) the film has a strain recovery of at least 18 mm, which provides excellent performance properties in stretch wrapping, especially in the area of high deformation recover.

What is claimed is: 
     
       1. A wrapping film of a polyolefin-based resin, wherein the film has the following properties: (1) a thickness ranging from 6 to 100 μm;   (2) a birefringence Δn A  ranging from 0.6×10 -3  to 8×10 -3 , said birefringence defined by equation:   Δn.sub.A =|n.sub.MD -n.sub.TD |        wherein n MD  is a refractive index in the machine direction, and n TD  is a refractive index in the transverse direction;   (3) a ratio S MD  /S TD  ranging from 0.65 to 1.50, wherein S MD  and S TD  are each heat shrinkage in the machine direction and that in the transverse direction when the film is allowed to stand in a silicone oil bath at 140° C. for 3 minutes; and   (4) a strain recovery of 18 mm or more, as determined by clamping a circular film specimen having a diameter of 100 mm, indenting at the center thereof with a hemispherical indenter 20 mm in diameter to cause deformation, and measuring the maximum strain which disappears completely upon removal of the indenter.   
     
     
       2. A wrapping film as claimed in claim 1, wherein film has a tensile modulus of from 600 to 1400 kg/cm 2  in both machine and transverse directions. 
     
     
       3. A wrapping film as claimed in claim 1, wherein said film has a ratio of stress at 50% elongation in the machine direction (T MD ) to stress at 50% elongation in the transverse direction (T TD ) of from 0.50 to 2.50. 
     
     
       4. A wrapping film as claimed in claim 1, wherein said film has a ratio of percent heat shrinkage in the machine direction (S MD ) to percent heat shrinkage in the transverse direction (S TD ) of from 0.7 to 1.35. 
     
     
       5. A wrapping film as claimed in claim 1, wherein said film is a blown film obtained by inflating, at a blow-up ratio of from 9 to 20, a laminate tubular film having an intermediate layer comprising a linear low-density polyethylene-based resin having an MFR of from 0.1 to 5 g/10 min and a Q-value of from 1 to 6, wherein said intermediate layer has laminated on both sides thereof a surface Layer comprising a copolymer resin comprising from 60 to 95% by weight of ethylene-based structural units and from 5 to 40% by weight of structural units derived from a monomer selected from the group consisting of vinyl acetate, aliphatic unsaturated carboxylic acids, and aliphatic unsaturated carboxylic acid alkyl esters. 
     
     
       6. A wrapping film as claimed in claim 5, wherein said blown film has a total thickness of from 8 to 30 μm. 
     
     
       7. A wrapping film as claimed in claim 6, wherein said intermediate layer has a thickness of from 2 to 10 μm and each surface layer has a thickness of from 3 to 10 μm. 
     
     
       8. A wrapping resin film as claimed in claim 5, wherein said linear low-density polyethylene-based resin is a resin selected from the group consisting of ethylene-1-butene copolymers, ethylene-1-hexene copolymers, ethylene-1-butene-1-hexene copolymers, ethylene-4-methyl-1-pentene copolymers, ethylene-1-hexene copolymers, and ethylene-1-octene copolymers, wherein said resin has a density of from 0.89 to 0.93 g/cm 3 . 
     
     
       9. A wrapping film as claimed in claim 1, wherein said film is a blown film obtained by inflating, at a blow-up ratio of from 9 to 20, a laminate tubular film having an intermediate layer comprising from 80 to 95% by weight of a linear low-density polyethylene having an MFR of from 0.1 to 5 g/10 min and a Q-value of from 1 to 6 and from 5 to 20% by weight of a copolymer resin comprising from 60 to 95% by weight of ethylene-based structural units and from 5 to 40% by weight of structural units derived from a monomer selected from the group consisting of vinyl acetate, aliphatic unsaturated carboxylic acids, and aliphatic unsaturated carboxylic acid alkyl esters, wherein said intermediate layer has laminated on both sides thereof a surface layer comprising a copolymer resin comprising from 60 to 95% by weight of ethylene-based structural units and from 5 to 40% by weight of structural units derived from a monomer selected from the group consisting of vinyl acetate, aliphatic unsaturated carboxylic acids, and aliphatic unsaturated carboxylic acid alkyl esters. 
     
     
       10. A wrapping film as claimed in claim 9, wherein said blown film has a total thickness of from 8 to 30 μm. 
     
     
       11. A wrapping film as claimed in claim 10, wherein said intermediate layer has a thickness of from 2 to 10 μm and each surface layer has a thickness of from 3 to 10 μm. 
     
     
       12. A wrapping film as claimed in claim 9, wherein said linear low-density polyethylene-based resin is a resin selected from the group consisting of ethylene-1-butene copolymers, ethylene-1-hexene copolymers, ethylene-1-butene-1-hexene copolymers, ethylene-4-methyl-1-pentene copolymers, ethylene-1-hexene copolymers, and ethylene-1-octene copolymers, wherein said resin has a density of from 0.89 to 0.92 g/cm 3 . 
     
     
       13. A wrapping film as claimed in claim 1, wherein, said film is a blown film obtained by inflating, at a blow-up ratio of from 8 to 20, a laminate tubular film having an intermediate layer comprising from 10 to 90% by weight of a crystalline polyolefin-based resin selected from the group consisting of ethylene-based resins and propylene-based resins and from 10 to 90% by weight of an olefinic thermoplastic elastomer, wherein said intermediate layer has laminated on both sides thereof a surface layer comprising a copolymer resin comprising from 60 to 95% by weight of ethylene-based structural units and from 5 to 40% by weight of structural units derived from a monomer selected from the group consisting of vinyl acetate, aliphatic unsaturated carboxylic acids, and aliphatic unsaturated carboxylic acid alkyl esters. 
     
     
       14. A wrapping film as claimed in claim 13, wherein said blown film has a total thickness of from 8 to 30 μm. 
     
     
       15. A wrapping film as claimed in claim 14, wherein said intermediate layer has a thickness of from 2 to 10 μm and each surface layer has a thickness of from 3 to 10 μm. 
     
     
       16. A wrapping film as claimed in claim 5, wherein said surface layer or intermediate layer or both further contains at least one additive selected from the group consisting of lubricants, tackifiers, and nucleating agents. 
     
     
       17. A wrapping film as claimed in claim 9, wherein said surface layer or intermediate layer or both contains at least one additive selected from the group consisting of lubricants, tackifiers, and nucleating agents. 
     
     
       18. A wrapping film, as claimed in claim 13, wherein said surface layer or intermediate layer or both further contains at least one additive selected from the group consisting of lubricants, tackifiers, and nucleating agents. 
     
     
       19. A wrapping film as claimed in claim 16, wherein said at least one additive is present in a total amount of from 0.5 to 5% by weight. 
     
     
       20. A wrapping film as claimed in claim 17, wherein said at least one additive is present in a total amount of from 0.05 to 5% by weight. 
     
     
       21. A wrapping film as claimed in claim 18, wherein said at least one additive is present in a total amount of from 0.05 to 5% by weight. 
     
     
       22. A wrapping film as claimed in claim 16, wherein said lubricant is a compound selected from the group consisting of oleamide, stearamide, erucamide, glycerol monostearate, glycerol distearate, glycerol monooleate, glycerol dioleate, and a polyethylene glycol adduct of the glyceride. 
     
     
       23. A wrapping film as claimed in claim 17, wherein said lubricant is a compound selected from the group consisting of oleamide, stearamide, erucamide, glycerol monostearate, glycerol distearate, glycerol monooleate, glycerol dioleate, and a polyethylene glycol adduct of the glyceride. 
     
     
       24. A wrapping film as claimed in claim 18, wherein said lubricant is a compound selected from the group consisting of oleamide, stearamide, erucamide, glycerol monostearate, glycerol distearate, glycerol monooleate, glycerol dioleate, and a polyethylene glycol adduct of the glyceride. 
     
     
       25. A wrapping film as claimed in claim 16, wherein said tackifier is a compound selected from the group consisting of castor oil derivatives, low-molecular viscous polybutylenes, and sorbitan higher fatty acid esters containing from 12 to 22 carbon atoms in the higher fatty acid moiety. 
     
     
       26. A wrapping film as claimed in claim 17, wherein said tackifier is a compound selected from the group consisting of castor oil derivatives, low-molecular viscous polybutylenes, and sorbitan higher fatty acid esters containing from 12 to 22 carbon atoms in the higher fatty acid moiety. 
     
     
       27. A wrapping film as claimed in claim 18, wherein said tackifier is a compound selected from the group consisting of castor oil derivatives, low-molecular viscous polybutylenes, and sorbitan higher fatty acid esters containing from 12 to 22 carbon atoms in the higher fatty acid moiety. 
     
     
       28. A wrapping film as claimed in claim 16, wherein said nucleating agent is talc or silica powder. 
     
     
       29. A wrapping film as claimed in claim 17, wherein said nucleating agent is talc or silica powder. 
     
     
       30. A wrapping film as claimed in claim 18, wherein said nucleating agent is talc or silica powder.